Electrical discharge device



May 5, 1964 G. LEWIN ELECTRICAL DISCHARGE DEVICE Filed Aug. 11, 1961 I II INVENTOR. GERHARD LEWIN BY wz m gaaw 3,132,279 ELECTRICAL DISCHARGEDEVICE Gerhard Lewin, West Orange, N .J., assignor to Engelhard-Hanovia, Inc, Newark, N.J., a corporation of New Jersey Filed Aug. 11,1961, Ser. No. 130,990 3 Claims. (Cl. 313-490) The present inventiondeals with an electrical device and more particularly with an electricaldischarge device in combination with a particular electrode and lead-inconductor construction.

Dicharge devices such as electrical gaseous discharge lamps having afused quartz or high temperature glass envelope containing a filling ofa rare gas, e.g., xenon, or a rare gas and a vaporizable metal, e.g.,mercury, are provided with at least a pair of spaced electrodescontained by the envelope and connected to a source of electricalcurrent by means of lead-in conductors, e.g. tungsten conductors,hermetically sealed through the lamp envelope. The quartz-to-metalhermetic seal is a critical significance since the lamps operate at hightemperatures and the difference in co-efficients of expansion of themetal and the quartz induces mechanical stresses which tend to crack thequartz and destroy the hermetic seal. When the hermetically sealedlead-in conductor is a thin wire of less than about 20 microns indiameter, it is possible to provide an adequate hermetic seal directlywith the quartz of the envelope, but such thin wires are disadvantageousin that they cannot carry appreciable current loads. For the desirableheavier current loads required by discharge lamps having a filling of,e.g., xenon or xenon and mercury, the thin lead-in conductors areinadequate. Heavier tungsten lead-in conductors cannot be suitablyhermetically sealed directly to the quartz of the envelope. Heaviertungsten lead-in conductors can be hermetically sealed through the wallof a fused quartz envelope, for example, when a leached seal or gradedseal as known in the manufacture of high pressure are lamps is employedbetween the lead-in conductor and the fused quartz of the lamp envelope.or graded seal constitutes an expansion transition means having aco-efiicient of expansion between that of the tungsten lead-in and thequartz of the envelope, with the transition means being located adjacentthe tungsten leadin and having a co-efiicient of expansion appropriatingthat of the tungsten. At least one layer of an aluminaborosilicate glassmay be employed as an expansion transition glass. However, such lead-inconductors as known are disadvantageous in that they provide a steeptemperature gradient from the inner end'of the seal to the outer endwith the temperature difference between the two ends being excessive andcreating thermal stresses in the seal.

In accordance with the present invention, the abovementioneddisadvantage of the undesirable steep temperature gradient in the sealis substantially eliminated by a change of the electrical and thermalconduction of the 1ead-in conductor at the seal which operates tolocalize the high temperatures generated at the electrode and torestrict steep temperature gradients to the region within the envelope,whereby comparatively low temperature gradients are provided through theseal.

It is an object of the invention to provide an electrical discharge lamphaving a lead-in conductor hermetically sealed through the lamp envelopeand including means to reduce the temperature gradient through the lampseal.

It is another object of the invention to provide an electrode andlead-in conductor construction for electrical discharge devices, wherebyhigh temperature gradients are localized along selected portions of theconductor.

Other objects and advantages of the invention are be- In such case, theleached j 3 ,132,279 7 Patented May 5, 1964 ice coming apparent from thedescription hereinafter following and the drawings forming a part hereofin which: FIGURE 1 illustrates a partly cross-sectional and partlyelevational view of a discharge lamp according to the invention, and

FIGURE 2 illustrates a partly cross-sectional and partly elevationalfragmentary view of a modified form of discharge lamp;

Regarding the drawings,:FIGURE 1 illustrates an electrical dischargelamp 1 having an elongated envelope 2,

composed of fused quartz. The lamp envelopenis provided with anionizable atmosphere of a rare gas or a rare gas and a vaporizablemetal. The atmosphere may consist of, for example, .xenon or xenon andmercury. The ends of the quartz envelope 2 are provided with axialopenings 3 and 4 whichv are capped with an assembly comprising a lead-inconductor, electrode and expansion transition seal means. The lead-inconductor comprises a first wire or a rod portion 5 and a second wire orrod portion 6 extending preferably axially of the first portion,

the first portion, as illustrated by FIGURE 1, being of.

larger diameter than the second portion. For example, the first portionhas a cross-sectional area about 3 to 4 times that of the secondportion. An electrode 7 is mounted on the end of the second portion ofthe conductor, with the electrode being of substantial mass and having across-sectional area substantiallygreater than the second conductorportion.

The first conductor portion 5 is coated with a layer 8 of a glass havinga co-efiicient of expansion approximately that of the metal of which theportion 5 is composed, e.g. tungsten. At least one layer 8, 9 and 10 ofa transition glass material is fused to the opening 3 and 4 of theenvelope 2, thereby hermetically sealing the envelope at both ends.While electrodes 7 are illustrated as identical electrodes for lampsemploying alternating current, the electrodes may also be dimensionedwith one being of greater mass than the other for direct currentoperated lamps. Regarding the electrode and lead-in conductor assemblyillustrated by FIGURE 1, the first portion 5 of the conductor may have alength of about one-half inch and a diameter of about .12 inch and thesecond portion 6 may have a length of about one inch and a diameter ofabout .06 inch. This yields the mini-' mum heat flow for a current of 50amp. The electrode 7 is dimensioned to have sufficient mass to maintaina 7 low evaporization rate of the electrode metal.

ence between the two ends of portion 6. Consequently,

the temperature along portion 5 is uniformly low and almost equal to thetemperature of the outside end of portion 5. Therefore, the lamp can beeffectively water cooled without creating thermal stresses at the seal.

The cross section of the portion 5 is about 4 times larger than that ofportion 6. This increases the thermal conduction more than 4 fold andreduces the Joule heat generated in this portion resulting in anegligible temperature drop through the portion 5 within the seal areaof glass layer 8.

FIGURE 2 illustrates a modification of the invention and comprises anelongated fused quartz envelope and seal construction identical to thatdescribed with respect to FIGURE 1. However, the lead-in conductorcomprises a heat conduction varying means of dilferent form.

3 In FIGURE 2, the lead-in conductor comprises a first conductor portion11 and a second portion 12 extending preferably axially outwardly of thefirst portion 11. An electrode 13 is mounted at the end of the secondportion. The second portion 12, as illustrated, has a cross-sectionalarea equal to that of portion 11, but the first portion is composed of ametal of higher heat and electrical conductivity than the portion 12.For example, the first portion is composed of tungsten and the secondportion is composed of tantalum. With this construction, the

steep temperature gradients occur along the portion of lower heatconductivity and within the envelope 2 with the result that a smallertemperature drop occurs through the portion 11 passing throughseal'component 8.

Various modifications of the invention are contemplated within the scopeof the appended claims.

What is claimed is:

1. An electrical discharge device comprising a light transmissiveenvelope containing an ionizable atmosphere, a conductor extendingthrough the envelope wall into the envelope, said conductor comprising afirst portion sealed through the envelope wall and a second portionextending into the envelope from the first portion with an electrodeelement on the inward end of the second portion, the cross-sectionalarea of the first and second portions being substantially equal, andsaid first portion being made of material having higher heat andelectrical conductivity than the second portion whereby the secondportion has a steeper temperature gradient than the first portion.

2. An electrical discharge device according to claim 1 in which thefirst portion of the conductor is made of tungsten and the secondportion is made of tantalum.

3. An electrical discharge device according to claim 1 includingexpansion transition material between the said first portion and theenvelope wall.

References Cited in the file of this patent UNITED STATES PATENTS

1. AN ELECTRICAL DISCHARGE DEVICE COMPRISING A LIGHT TRANSMISSIVEENVELOPE CONTAINING AN IONIZABLE ATMOSPHERE, A CONDUCTOR EXTENDINGTHROUGH THE ENVELOPE WALL INTO THE ENVELOPE, SAID CONDUCTOR COMPRISING AFIRST PORTION SEALED THROUGH THE ENVELOPE WALL AND A SECOND PORTIONEXTENDING INTO THE ENVELOPE FROM THE FIRST PORTION WITH AN ELECTRODEELEMENT ON THE INWARD END OF THE SECOND PORTION, THE CROSS-SECTIONALAREA OF THE FIRST AND SECOND PORTIONS BEING SUBSTANTIALLY EQUAL, ANDSAID FIRST PORTION BEING MADE OF MATERIAL HAVING HIGHER HEAT ANDELECTRICAL CONDUCTIVITY THAN THE SECOND PORTION WHEREBY THE SECONDPORTION HAS A STEEPER TEMPERATURE GRADIENT THAN THE FIRST PORTION.